Sadie Gurman

Danita Sienknecht was on a car ride with her husband one recent morning when a stranger called her with an outlandish offer. If she wired him $4,000 overnight, someone would show up at her door the next morning with two doses of a coveted coronavirus vaccine she knew doesn’t exist.

The caller, who knew her name, said he was at a Holiday Inn not far from her southwest Missouri home and told the 84-year-old to send the money right away. He called her 29 more times when she refused to call back.